Hull Failure?

Decked Canoes, Open Canoes, as long as they're canoes!

Moderators: kenneth, sbroam, TheKrikkitWars, Mike W., Sir Adam, KNeal, PAC, adamin

Post Reply
Carol
C Guru
Posts: 148
Joined: Fri Jul 20, 2007 1:37 am
Location: Eureka, Calif

Hull Failure?

Post by Carol »

Has anybody come across this before?

This spring, when we brought out our Dagger Dimension to be cleaned up after winter storage, we noticed 2 cracks both about 4 inches long about a foot in front of the stern pedestal seat about in the area where the center airbags end. One crack went lengthwise, the other side to side. There was no visible signs of damage on the outside hull. The last time we had used the boat, previous summer, we had not come down on any rocks in that area that we could remember.

Then this weekend while visiting our friend with a Dagger Genesis, he showed us similar cracks in his boat. The first set were in the stern under his airbags, both ran lengthwise and about 3 inches long. The second set of cracks were just in front of his Bob Foote saddle, right side, in the area where he would bail. These cracks were more of a star pattern, but again, with both sets of cracks there wasn't any visible sign on the outside of the hull of severe impacts. With the Genesis, though, it had just come off of the Middle Fork of the Salmon where it had been used and slightly abused. But it's also possible that these cracks predated the trip, as the airbags had not been out of the boat before the Middle Fork in over five years

The Dimension is 18 years old, had been stored inside in a Sacramento, California garage for the first 15 years, and basically wasn't used. We purchased it in 2004 and store it in a shed in Eureka, north coast of California (year-round temperatures average between high 30° to 60°), and usually use it on one extended outing a year (for every day paddling, we use a different Dimension-but that's a different story).

The Genesis I believe was purchased in 1992, and is stored in Redding, California (year-round temperatures average between high 30° to 100° plus) outside, but out of the direct sun.

So the big questions: Are these hulls starting to break down due to age?
How best to repair them?
On the Dimension , I cut large pieces of raft material and Vyna- bonded them over the cracks. In the Genesis, he worked "Goop" into the cracks. We would appreciate any input on how to deal with this if they continue to appear..

Thanks, happy paddling,

Carol
ezwater
C Maven
Posts: 1652
Joined: Wed Feb 26, 2003 12:43 am
Location: Decatur, GA

Post by ezwater »

Be careful about using Vynabond in a way where it can get at the ABS beneath the vinyl. Clearly it COULD access the ABS through the cracks you were patching.

I have not experienced inside cracking on my ABS boats, which included a very old OT Tripper. I think cracking can reflect just the stretching of the inner ABS layer beyond its limit of tension. A complete crack of the outer ABS layer should show up, but a partial, inside crack in the outer ABS layer might be hidden by the vinyl outer layer.

Any and all outfitting features that restrict the ability of the ABS to bend inward on a broad front when impacted, MAY result in stretching of the inner layer of ABS beyond its splitting point.

My experience with plastics in general indicates that they may become more brittle with age. I saw an old Mad River ME split raggedly down the stem when it slid down a very steep bank into a tree. If the boat had not been old, I think a crimped and folded form of damage would have resulted instead.

Eric Nyre, who posts on paddling.net, says that the real aging factor with Royalex is degrading and stiffining of the center foam layer because of cumulative water infiltration. He is less certain about whether the ABS becomes brittle.

I think the most effective patching method for cracks in ABS is to skim the vinyl off with a low angle sharp chisel, and then to apply concentric cloth patches (Kevlar for inside, glass for outside), the LARGEST patch first, using West epoxy. It will take at least a three layer patch, up to a five layer patch for a big, through-crack.

If you choose to use patch materials like ABS sheet or Kydex (a vinyl), I suggest using a urethane glue such as 3M Structural Adhesive. Vynabond is dangerous to use around exposed ABS.
Carol
C Guru
Posts: 148
Joined: Fri Jul 20, 2007 1:37 am
Location: Eureka, Calif

Hull repair

Post by Carol »

I'm guessing your concerns regarding vynabond is because it would dissolve the foam layer?

My concerns for using Kevlar with glass overlay would be that it would make the hull too rigid. The Dimension is a 16 foot WW OC2, and having a rigid patch in the middle the boat sounds like it would seriously compromise the flexibility.

Thank you for the link to paddling.net.
ezwater
C Maven
Posts: 1652
Joined: Wed Feb 26, 2003 12:43 am
Location: Decatur, GA

Post by ezwater »

No, my concern about the Vynabond is that its solvent will soften ABS. Its effect on the foam is unknown to me.

Properly sized and concentricized Kevlar patches will not make a Royalex hull dangerously rigid in any way. Some Kevlar patch jobs I have seen may have that effect, because the patchers lay three or more layers smack on top of one another without using the concentric patch principle, so that there are sharp transition zones at the edge of the patch.

To be effective, whatever patch is used must, in its center region, be about as stiff as the cracked ABS beneath it. For a really custom job, one should thin and taper the ABS toward the crack, but I think this is usually unnecessary.

If something does not stiffen your hull where those cracks are, the cracks will expand with further stress. Cloth/vinyl patches are not going to stiffen the hull. They are just bandaids.
User avatar
yarnellboat
C Maven
Posts: 1331
Joined: Wed Apr 06, 2005 8:54 pm
Location: Winnipeg
Contact:

Post by yarnellboat »

Hi,

Yes. My Outrage has a problem with these inner hairline cracks. I assumed it was because it's old and may have been stored in the sun (I bought used from a rental shop), but a friend's newer Outrage has similar cracks - but we're both heavy guys paddling boney rivers.

There's long threads on it here somewhere.

For areas with multiple cracking and ongoing stress (at my saddle-front and knees), I put down a thin sheet of ABS plastic on the inside of the hull. Glued it in with the standard 2-part 3M urethane adhesive.

For single cracks, I drill the ends, cut out or grind out the crack a bit and fill it (and I also did that for the cracks that I put under the ABS plate too). After trying various epoxies and adhesives (all too brittle and prone to re-cracking, or creating an adjacent crack), I've now just gone to filling the cracks with simple Goop.

PY.
Carol
C Guru
Posts: 148
Joined: Fri Jul 20, 2007 1:37 am
Location: Eureka, Calif

Post by Carol »

I would like to say thanks to everybody who responded to my query. Next time I should ask for advice before I try to do something I don't know anything about.

Happy paddling

Carol
Post Reply